The answer to that is complex, but worth considering what happens without it. A perfect example would be the Bill Hicks guest appearance on David Letterman that was not allowed to air because the material was considered too sensitive.

http://www.youtube.com/watch?v=pkptz2YfZik

http://www.youtube.com/watch?v=vf340K_Ed0o&feature=relat...

I fullheartedly support comedy as a form of free speech that should not be influenced by sponsorship.

Remember: Nothing is free. If something is "free", that's because it's you that's being sold.